LibJS: Add Object.{isExtensible,preventExtensions}()

Author: https://github.com/mattco98
Commit: https://github.com/SerenityOS/serenity/commit/d5ae73a63b0
Pull-request: https://github.com/SerenityOS/serenity/pull/2474

Libraries/LibJS/Runtime/Object.cpp

@@ -89,6 +89,12 @@ bool Object::has_prototype(const Object* prototype) const
     return false;
 }
 
+bool Object::prevent_extensions()
+{
+    m_is_extensible = false;
+    return true;
+}
+
 Value Object::get_own_property(const Object& this_object, PropertyName property_name) const
 {
     Value value_here;
@@ -308,6 +314,13 @@ bool Object::put_own_property(Object& this_object, const FlyString& property_nam
 {
     ASSERT(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));
 
+    if (!is_extensible()) {
+        dbg() << "Disallow define_property of non-extensible object";
+        if (throw_exceptions && interpreter().in_strict_mode())
+            interpreter().throw_exception<TypeError>(String::format("Cannot define property %s on non-extensible object", property_name.characters()));
+        return false;
+    }
+
     if (value.is_accessor()) {
         auto& accessor = value.as_accessor();
         if (accessor.getter())
@@ -375,6 +388,13 @@ bool Object::put_own_property_by_index(Object& this_object, u32 property_index,
 {
     ASSERT(!(mode == PutOwnPropertyMode::Put && value.is_accessor()));
 
+    if (!is_extensible()) {
+        dbg() << "Disallow define_property of non-extensible object";
+        if (throw_exceptions && interpreter().in_strict_mode())
+            interpreter().throw_exception<TypeError>(String::format("Cannot define property %d on non-extensible object", property_index));
+        return false;
+    }
+
     if (value.is_accessor()) {
         auto& accessor = value.as_accessor();
         if (accessor.getter())

Libraries/LibJS/Runtime/Object.h

@@ -98,6 +98,9 @@ public:
     void set_prototype(Object*);
     bool has_prototype(const Object* prototype) const;
 
+    bool is_extensible() const { return m_is_extensible; }
+    bool prevent_extensions();
+
     virtual Value value_of() const { return Value(const_cast<Object*>(this)); }
     virtual Value to_primitive(Value::PreferredType preferred_type = Value::PreferredType::Default) const;
     virtual Value to_string() const;
@@ -122,6 +125,7 @@ private:
     void set_shape(Shape&);
     void ensure_shape_is_unique();
 
+    bool m_is_extensible { true };
     Shape* m_shape { nullptr };
     Vector<Value> m_storage;
     IndexedProperties m_indexed_properties;

Libraries/LibJS/Runtime/ObjectConstructor.cpp

@@ -48,6 +48,8 @@ ObjectConstructor::ObjectConstructor()
     define_native_function("getOwnPropertyNames", get_own_property_names, 1, attr);
     define_native_function("getPrototypeOf", get_prototype_of, 1, attr);
     define_native_function("setPrototypeOf", set_prototype_of, 2, attr);
+    define_native_function("isExtensible", is_extensible, 1, attr);
+    define_native_function("preventExtensions", prevent_extensions, 1, attr);
     define_native_function("keys", keys, 1, attr);
     define_native_function("values", values, 1, attr);
     define_native_function("entries", entries, 1, attr);
@@ -104,6 +106,26 @@ Value ObjectConstructor::set_prototype_of(Interpreter& interpreter)
     return {};
 }
 
+Value ObjectConstructor::is_extensible(Interpreter& interpreter)
+{
+    auto argument = interpreter.argument(0);
+    if (!argument.is_object())
+        return Value(false);
+    return Value(argument.as_object().is_extensible());
+}
+
+Value ObjectConstructor::prevent_extensions(Interpreter& interpreter)
+{
+    auto argument = interpreter.argument(0);
+    if (!argument.is_object())
+        return argument;
+    if (!argument.as_object().prevent_extensions()) {
+        interpreter.throw_exception<TypeError>("Proxy preventExtensions handler returned false");
+        return {};
+    }
+    return argument;
+}
+
 Value ObjectConstructor::get_own_property_descriptor(Interpreter& interpreter)
 {
     auto* object = interpreter.argument(0).to_object(interpreter);

Libraries/LibJS/Runtime/ObjectConstructor.h

@@ -48,6 +48,8 @@ private:
     static Value get_own_property_names(Interpreter&);
     static Value get_prototype_of(Interpreter&);
     static Value set_prototype_of(Interpreter&);
+    static Value is_extensible(Interpreter&);
+    static Value prevent_extensions(Interpreter&);
     static Value keys(Interpreter&);
     static Value values(Interpreter&);
     static Value entries(Interpreter&);

Libraries/LibJS/Tests/Object.isExtensible.js

@@ -0,0 +1,22 @@
+load("test-common.js");
+
+try {
+    assert(Object.isExtensible() === false);
+    assert(Object.isExtensible(undefined) === false);
+    assert(Object.isExtensible(null) === false);
+    assert(Object.isExtensible(true) === false);
+    assert(Object.isExtensible(6) === false);
+    assert(Object.isExtensible("test") === false);
+
+    let s = Symbol();
+    assert(Object.isExtensible(s) === false);
+
+    let o = { foo: "foo" };
+    assert(Object.isExtensible(o) === true);
+    Object.preventExtensions(o);
+    assert(Object.isExtensible(o) === false);
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}

Libraries/LibJS/Tests/Object.preventExtensions.js

@@ -0,0 +1,48 @@
+load("test-common.js");
+
+try {
+    assert(Object.preventExtensions() === undefined);
+    assert(Object.preventExtensions(undefined) === undefined);
+    assert(Object.preventExtensions(null) === null);
+    assert(Object.preventExtensions(true) === true);
+    assert(Object.preventExtensions(6) === 6);
+    assert(Object.preventExtensions("test") === "test");
+
+    let s = Symbol();
+    assert(Object.preventExtensions(s) === s);
+
+    let o = { foo: "foo" };
+    assert(o.foo === "foo");
+    o.bar = "bar";
+    assert(o.bar === "bar");
+
+    assert(Object.preventExtensions(o) === o);
+    assert(o.foo === "foo");
+    assert(o.bar === "bar");
+
+    o.baz = "baz";
+    assert(o.baz === undefined);
+
+    Object.defineProperty(o, "baz", { value: "baz" });
+    assert(o.baz === undefined);
+
+    assertThrowsError(() => {
+        "use strict";
+        o.baz = "baz";
+    }, {
+        error: TypeError,
+        message: "Cannot define property baz on non-extensible object",
+    });
+
+    assertThrowsError(() => {
+        "use strict";
+        Object.defineProperty(o, "baz", { value: "baz" });
+    }, {
+        error: TypeError,
+        message: "Cannot define property baz on non-extensible object",
+    });
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}